(1) Field of the invention
The present invention generally relates to a signal reproducing apparatus for reproducing a signal, such as an audio signal, from a recording medium, such as a DAT (Digital Audio Tape), and more particularly to a signal reproducing apparatus in which a signal can be rapidly and precisely reproduced starting from a leading edge of the signal. In addition the present invention relates to a unit capable of precisely detecting leading edges of various signals.
(2) Description of related art
Conventionally, for example, when an audio signal is recorded in a DAT, an identification signal, a so called start ID, is also recorded at a starting position of the audio signal. The audio signal is then reproduced starting from a position at which the start ID is detected. However, in many cases, a position at which the start ID is recorded in the DAT differs from an actual leading edge of the audio signal, at which leading edge the audio signal is activated. Thus, in a signal reproducing apparatus for the DAT, a recording position of the start ID can be changed by manual operations while listening to a music output by the reproduction of the audio signal.
In a CD (Compact Disk) on which tracks Tr are formed as shown in FIG. 1, a start ID is recorded in a starting position of an audio signal, but a position at which the start ID is recorded is not coincident with the actual leading edge of the audio signal. In a conventional CD player by which audio signals are reproduced from the CD 1, the signal reproduction in a track Tr.sub.o in which the start ID is recorded is repeatedly performed. While the signal reproduction is being repeated, a position at which the level of a reproduction signal is greatly changed in the CD 1 is detected, and the position is stored in a memory. When a start operation of the reproduction is performed, the audio signal is reproduced, independently the start ID, from the position stored in the memory.
The above process performed in the CD player may be applied to the signal reproducing apparatus for the DAT so that the start position at which the signal is to be reproduced from the DAT is rectified.
However, because the DAT is a tape shaped recording medium, a long time is required to repeat the signal reproduction in a predetermined region on the DAT, which region includes a position at which the start ID is recorded. In addition, as the leading edge of the signal is identified by a position on the DAT (the recording medium), it is difficult to rapidly reproduce the audio signal from the detected position identified as the position on the DAT when the start operation is performed.
In the signal reproducing apparatus for the DAT, the following technique has been proposed. That is, an audio signal recorded in a predetermined region on the DAT, which region includes the start ID, is stored in a memory, and the audio signal is then read out from a position, in the memory, corresponding to the start ID when the starting operation is performed. If the above technique is used, the audio signal can be rapidly reproduced starting from the leading edge thereof.
However, to detect the leading edge of the audio signal in the recording medium (the DAT), the signal reproduction must be repeated, as described above, and further, the signal recorded in a predetermined region must be reproduced again and then stored in the memory. Thus, a long time is required for making a state in which the reproduction signal can be output.
In addition, the audio signals to be stored in the recording medium such as the DAT include various background signals (noises). Levels of background signals under a silent condition in which there is no audio signal corresponding to a music differ from each other based on recording conditions. Thus, in a case where the leading edge of the signal is detected using a single reference level, it is difficult to precisely detect the leading edges of various signals which has been recorded under conditions in which different background signals (noises) are included in the signals.